Coffee consumption and cardiovascular outcomes: cautionary or causal?

We read with interest the study by Chieng et al.,1 on the impact of coffee subtypes and incidence of cardiovascular disease, arrythmias, and mortality. Among the pool of coffee drinkers, this study assessed the outcomes of drinking up to five cups of coffee/day. Their results show a reduction in cardiovascular mortality, among those who drink up to five cups/day. The hazard ratios for the risks of cardiovascular mortality, cardiovascular disease (CVD), and any arrythmia with four to five cups of coffee use were reported as 0.89 [95% confidence interval (CI) 0.80–0.98], 0.93 (95% CI 0.90–0.96), and 0.93 (95% CI 0.88–0.97), respectively. Considering the extent of interest this subject has drawn in the media, several limitations of this study warrant discussion. First, unmeasured confounding might have affected the results. One major unmeasured confounder for this question that was not controlled for in the study is physical activity, which is a common cause of coffee drinking and cardiovascular disease2 (Figure 1).